/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;
​
    Node() {}
​
    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    int maxDepth(Node* root) {
        if(!root) return 0;
        int res=0;
        for(auto i:root->children)
            res=max(res,maxDepth(i));
        return ++res;
    }
};